It is known that certain types of equipment have output characteristics with a tendency to change as the equipment ages. In particular, electromechanical resonators, e.g., piezoelectric crystals, have resonant frequency characteristics which vary due to temperature and aging of the resonator. The variations have a tendency to cause shifts in an output frequency of an oscillator including a particular resonator. Many systems and methods have been devised for automatically compensating for the variations due to temperature. However, compensation for variations due to aging have generally employed manual techniques or electromechanical devices. The manual techniques and electromechanical devices employed for compensating for aging of an electromechanical resonator have generally involved from time to time comparing the output frequency of an oscillator controlled by the resonator with a standard frequency. In response to a deviation between the oscillator and standard frequencies, the frequency of the oscillator is varied with an electromechanically controlled reactor or by manual adjustment of a reactor. The electromechanical and manual aging adjustments both have serious disadvantages.
Unattended or remote equipment containing electromechanical resonators can not be manually adjusted in many instances. This is particularly true for equipment located on space craft or at other remote monitoring sites. Manual adjustment of equipment that is not remote or which is susceptible to being attended requires circuitry associated with the electromechanical resonator to be open to atmospheric contaminants and corrosion, leading to further instabilities and reduced reliability of the electromechanical resonator, as well as other components associated with the resonator. Human error leading to inaccurate adjustment is another possible problem with manual maintenance of circuitry associated with the electromechanical resonator. Manual adjustment of the resonator to compensate for aging also requires maintenance records to be kept; historically such records have been manually kept, with the possible problems of error and loss.
Electromechanical control of reactors for compensating aging of electromechanical resonators is subject to microphonics which introduces noise and errors in the circuitry associated with the resonators. In addition, electromechanical control of such reactors usually requires significant amounts of power and is likely to require circuitry associated with the resonator to be open to atmospheric contaminants and corrosion.
Another problem with the prior art aging compensating apparatus and methods for variations due to aging in resonant frequency characteristics of electromechanical resonators is that the oscillator associated with the resonator must usually be disconnected from the equipment being driven by the oscillator. Thus, such equipment is not operational during the time while the aging compensation is being performed. Removing the oscillator containing the electromechanical resonator from the equipment being driven by the resonator also may subject that equipment to damage.
It is, accordingly, an object of the present invention to provide a new and improved apparatus for and method of compensating for variations due to aging in output characteristics of equipment.
Another object of the present invention is to provide a new and improved method of and apparatus for compensating for aging variations of electromechanical resonators.
An added object of the present invention is to provide a new and improved method of and apparatus for compensating for aging variations of electromechanical resonators wherein circuitry associated with the resonator is closed to atmospheric contaminants and corrosion.
A futher object of the invention is to provide a new and improved apparatus for and method of automatically compensating for variations due to aging of an electromechanical resonator by using all electronic, low power consuming means.
Still another object of the invention is to provide a new and improved apparatus for and method of compensating for aging of an electromechanical resonator wherein an oscillator driven by the resonator remains in operation while the frequency thereof is compensated.
A further object of the invention is to provide a new and improved apparatus for and method of compensating for aging variations of electromechanical resonators by utilizing extremely low power consuming components which contribute to a highly accurate and stable output of an oscillator including the resonator.